安全不安全，因人而異。人體自身皮膚也含有玻尿酸。外用主要是為了保濕，但是滲透力有限，很難說有多大效用。。。參考：

Hyaluronic Acid – the Latest Beauty BuzzDifficulty: EasyRating:
By: Duncan Idaho
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If you’ve been following the latest skin care news you’ll have noticed there’s a new wonder ingredient on the market – hyaluronic acid. Used previously as an injectable treatment for lines and wrinkles in the form of dermal fillers like Restylane, hyaluronic acid is now available for topical application in a range of gels, serums and moisturisers.
These products claim to dramatically improve the appearance of the skin and by doing so pander to the desire many of us have to find youth in a bottle. But what is hyaluronic acid, how does it work, and how effective can simply rubbing it on the surface of your skin be?
A Prevalent Sugar
Hyaluronic acid is a complex sugar, known as a glycosaminoglycan, and is found throughout the body. It is particularly prevalent in connective tissue, the synovial fluid around joints, the eyes, the heart, the intervertebral spinal disks and the skin.
It transports nutrients to cells and removes toxins, it acts as a cushioning agent, it lubricates joints and, importantly for the skin care industry, it facilitates water retention in body tissue. In fact, hyaluronic acid can absorb more than one thousand times its weight in water.
In the Skin
Picture your dermis, that layer if inner tissue beneath the surface (or epidermis) of your skin, as a sponge. The solid parts of that sponge are the collagen and elastin fibres that form the supporting matrix of the skin, and the spaces within the sponge are where the skin’s gel-like hyaluronic acid sits. Obviously, if you can pack those spaces with more water-rich hyaluronic acid your skin will have a fuller, firmer, more youthful appearance.
Skin Aging
Over time, and through the effects of UV radiation and environmental pollutants, the ability of the skin to produce hyaluronic acid, at a high in adolescence and early adulthood, declines. As a result, the skin becomes dehydrated – there’s less of the water-retaining gel in our sponge example – and the collagen/elastin structure loses it’s integrity. The result? Thinning of the dermis, a loss of skin radiance, and the formation of lines and wrinkles.
Topical Effectiveness?
It’s no wonder, then, that the notion of replenishing the skin’s hyaluronic acid has become a popular focus for skin care companies and beauty enthusiasts alike. But can it be done by the topical application of hyaluronic acid gels and serums?
There are two areas those seeking more youthful-looking skin should consider:
1/ When used as a moisturiser for the surface of the skin (as opposed to dermal replenishment) it has been suggested that hyaluronic acid’s great affinity for water may, if it is used in high concentrations and in very dry climates, actually back-fire on the user by pulling moisture out of the skin – the exact opposite of what the product is intended to do.
2/ Much of the buzz around hyaluronic acid centres on its ability to rebuild the skin matrix – to plump out those spaces in our sponge. But can it actually penetrate that deeply? Hyaluronic acid molecules vary in size. As large molecules (those with a molecular weight over, say, 20,000 Daltons) cannot effectively penetrate the skin, a product that uses large molecule hyaluronic acid may be of limited value in replenishing dermal hyaluronic acid. In order for hyaluronic acid to penetrate the skin the molecule must be micronised, or chopped into fragments.
Youth in a Bottle
The prospect of transforming your skin, not just at its surface, but right down at its foundations, is a tantalising one. Who wouldn’t want smoother, more radiant, youthful-looking skin? But while the science of hyaluronic acid is sound – it’s a component of the skin matrix, it has a massive ability to hold moisture – its actual effectiveness as a topical application should be carefully researched by those seeking youth in a bottle, particularly as these skin care products are some of the more costly available.
Learn more about hyaluronic acid in this video.
Tags: beauty therapy, Skin Care
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• 因為滲透進入皮膚困難，美容科用它注射。。。 -禦用文人- ♀ (0 bytes) () 12/22/2014 postreply 08:18:27